It is well known that unsterile toothbrushes may contribute to the spread of disease. (Glass et al, "Toothbrush Contamination: A Potential Health Risk?", Quintessence International, vol. 17, No. 1, pp 39-42, 1986.) It is also well known that toothbrushes can be sterilized by exposure to microwave energy. (Rohrer et al, "Sterilization by Microwaves", ODA Journal, pp 29-31, Winter, 1985.) However, such exposure to microwave energy for prolonged time periods results in distortion and/or deformation of the nylon tooth brush bristles. (See, U.S. Pat. No. 5,040,260 to Michaels at column 1, lines 46-46.) If exposed to microwave energy for time periods insufficient to distort the nylon bristle, however, there is a risk that the toothbrush will not be sterilized.
It would therefor be highly desirable if a process were provided which enabled microwave energy (with its time-saving benefits) to be employed as a means of sterilizing thermoplastic appliances, particularly nylon-bristle toothbrushes, without distortion. It is towards fulfilling such a need that the present invention is directed.
Broadly, the present invention is embodied in a process by which microwave energy may be employed to sterilize thermoplastic appliances without distortion. According to the present invention, an appliance which is entirely, or includes components, formed of a thermoplastics material, e.g., conventional manual nylon-bristle toothbrushes or motor-assisted toothbrushes having metal components enclosed in a thermoplastics material (such as ORAL-B.RTM. toothbrushes or INTERPLAK.RTM. toothbrushes), may be sterilized by first bringing water contained in a reservoir of an uncovered sterilization tray to, or near, its boiling point by initial exposure to microwave energy. Thereafter, the appliance is placed in the sterilization tray in proximity to the microwave-preheated water. The sterilization tray may then be covered and subjected to an additional (shorter) cycle of microwave energy. During this subsequent microwave cycle, the water in the reservoir boils so that steam fills the covered container. The container is minimally pressurized by the steam (e.g., to less than about 10 psig, and usually less than 5 psig, due to the fact that the container's cover forms a fluid-tight seal). The steam and the microwave energy are sufficient to sterilize the toothbrush bristles. At the same time, however, since the time period during which the bristles of the toothbrush are exposed to the microwave energy is relatively short, no bristle deformation occurs. Alternatively, a damp toothbrush can be placed in a microwave device for longer periods of time without bristle deformity since the moisture on the damp toothbrush provides a source of steaming.
Further aspects and advantages of this invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.